Fig. 1: Sketch of the experiment. | Nature

Fig. 1: Sketch of the experiment.

From: Measurements of the gravitational constant using two independent methods

Fig. 1

a, In the TOS method, the pendulum is an Al-coated fused silica block with dimensions of 91 × 11 × 31 mm3 and mass of about 68 g. The pendulum is suspended by a thin fused silica fibre with a diameter of 40–60 μm and a length of 900 mm. The magnetic damper is suspended through a 50-mm-long, 80-μm-diameter tungsten fibre. Two SS316 stainless-steel spheres with an average diameter of 57.2 mm and a vacuum mass of 778 g are used as the source masses. A turntable is used to change the positions of the spheres between the ‘near’ and ‘far’ configurations (the ‘near’ configuration is shown here; in the ‘far’ configuration, the turntable is rotated by 90°). A hollow gold-coated aluminium cylinder installed between the pendulum and the spheres is used to shield the system from the electrostatic field. The pendulum and the source masses are placed inside the same vacuum chamber with a pressure of about 10−5 Pa maintained by an ion pump. The pendulum twist is monitored by an optical lever. b, In the AAF method, the pendulum is a gold-coated fused silica block with dimensions of 91 × 4 × 50 mm3 and a vacuum mass of 40 g. The main fibre is an 870-mm-long, 25-μm-diameter tungsten fibre. The design of the magnetic damper is the same as that in the TOS method. Four SS316 stainless-steel spheres with an average diameter of 127.0 mm and a vacuum mass of 8,541 g are used as the source masses that sit on an ULE-material shelf with upper and lower layers. The small deflection angle of the pendulum is recorded by an autocollimator. The chamber with the pendulum is hung under an air-bearing turntable, which is installed coaxially with the separate source-mass turntable. The apparatus are located in the passive thermal room situated in our cave laboratory.

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